Polyethylene wax

Abstract

Synthetic polyethylene wax having low molecular weight of 250 to 3000 and a density of 0.930 to 0.950 is prepared in a high pressure process at pressures of at least 800 bar using a carbonyl compound such as acetaldehyde as chain transfer agent. The resulting wax with incorporated CO has good compatibility in hot melt systems, and may be stripped to remove light ends, increase density and crystallinity and improve thermal stability.

We claim: 
     
       1. A process for the preparation of a polyethylene wax having Mn of from 250 to 3000 and a density of 0.930 to 0.950, comprising polymerizing ethylene at a pressure of at least 800 bar, at a temperature of from 150° to 270° C., in the substantial absence of solvent and in the presence of a carbonyl compound as chain transfer agent, forming the desired wax product, and treating the formed wax product to remove at least a part of the light end containing up to 34 carbon atoms. 
     
     
       2. A process as claimed in claim 1, in which the pressure is at least 1200 bar and the carbonyl compound is acetaldehyde. 
     
     
       3. A process as claimed in claim 2, in which the amount of acetaldehyde employed is from 5 to 15 wt. % based on the weight of the feed to the reactor. 
     
     
       4. A process as claimed in claim 2, in which the pressure in the polymerization reactor is in the range of from 1500 to 3000 bar. 
     
     
       5. A process as claimed in claim 1, in which the temperature of the reactor is in the range of 150° C. to 225° C. 
     
     
       6. A process as claimed in claim 1, in which the residence time in the reactor is from 20 to 120 seconds. 
     
     
       7. A process as claimed in claim 1, in which substantially all the light end containing up to 24 carbon atoms is removed by stripping. 
     
     
       8. A process as claimed in claim 7, in which from 8 to 10 wt. % of the wax is removed. 
     
     
       9. The process of claim 1 wherein the amount of carbonyl compound present is about 5 to 15 wt. % based on the weight of the feed through the reactor. 
     
     
       10. A process for the preparation of a thermally stable polyethylene wax having Mn of from 250 to 3000 and a density of 0.930 to 0.950, comprising: (1) polymerizing ethylene at a pressure of at least 800 bar, at a temperature of from 150° to 270° C., in the substantial absence of solvent and in the presence of from 5 to 15 wt. % based on the weight of the feed to the reactor of a carbonyl compound as chain transfer agent to give a wax product and (2) treating the wax product to remove at least a part of the light end containing up to 34 carbon atoms.